Final answer:
Physical changes refer to transformations where no new substances are formed, such as boiling water, which only changes from liquid to gas while remaining H₂O. Rusting of a nail is not a physical but a chemical change as iron reacts with oxygen to form iron oxide, a new substance.
Step-by-step explanation:
Identifying Physical Changes in an Experiment
In determining which changes are physical changes in an experiment, one should look for changes where no chemical bonds are broken or formed, meaning the molecular composition of the substance remains unchanged. For example, boiling water is a physical change.
When water boils, it transitions from a liquid to a gas (steam), but the molecules of H₂O remain the same before and after the change. This change could be represented as H₂O(l) → H₂O(g).
On the other hand, an example of a chemical change would be a nail rusting.
This occurs when the iron in the nail reacts with oxygen in the environment to form iron oxide (rust), represented by the chemical reaction Fe + O₂ → Fe₂O₃.
The formation of rust is indicative of a new product being formed, which is a clear sign of a chemical change.
Overall, a physical change might include a state change, such as melting, boiling, or breaking an object, where the substance's innate properties do not change.
In contrast, a chemical change results in new substances with different properties.